music

length := func(s string) time.Duration {
	d, err := time.ParseDuration(s)
	if err != nil {
		panic(s)
	}
	return d
}
var tracks = []*Track{
	{"Go", "Delilah", "From the Roots Up", 2012, length("3m38s")},
	{"Go", "Moby", "Moby", 1992, length("3m37s")},
	{"Go Ahead", "Alicia Keys", "As I Am", 2007, length("4m36s")},
	{"Ready 2 Go", "Martin Solveig", "Smash", 2011, length("4m24s")},
}
fmt.Println("Click Artist once:")
sort.Sort(ByTitle(tracks))
PrintTracks(tracks)
fmt.Println("Click Artist twice:")
sort.Sort(sort.Reverse(ByTitle(tracks)))
PrintTracks(tracks)
fmt.Println("Click Year once:")
sort.Sort(ByYear(tracks))
PrintTracks(tracks)
fmt.Println("Click Year twice:")
sort.Sort(sort.Reverse(ByYear(tracks)))
PrintTracks(tracks)
fmt.Println("Custom sorting: Title, Year, Length:")
sort.Sort(CustomSort{t: tracks, less: func(x, y *Track) bool {
	if x.Title != y.Title {
		return x.Title < y.Title
	}
	if x.Year != y.Year {
		return x.Year < y.Year
	}
	if x.Length != y.Length {
		return x.Length < y.Length
	}
	return false
}})
PrintTracks(tracks)

Output: